A number of electronic devices can benefit from the availability of information indicating one or more temperatures of the electronic device (or portions thereof). In at least some cases, it can be valuable to provide such temperature estimate information with a relatively high degree of accuracy and/or a relatively small time lag between a measurement and the output of an estimate. In at least some cases, it can be valuable to provide such temperature estimate information with relatively high frequency.
Although the present invention can be applied in any of a number of types of electronic devices, one example of an electronic device in which accurate, frequent and prompt temperature estimates are believed particularly valuable is in hard disk drives (HDD) including the types typically used in, or with, personal computers.
A number of aspects of HDD operation are temperature-related. Knowledge of ambient or head-disk assembly (HDA) temperature can be useful in at least some approaches to flying height adjustment. In a typical HDD, it is important to maintain the read/write head a predetermined distance (“flying height”) from the adjacent disk surface. Recent trends have been toward providing HDD's with relatively smaller flying heights (generally associated with attempts to increase areal data density in HDD's) and the tolerance for the flying height generally decreases as the flying height itself decreases. The thermal expansion effect known as “pole tip protrusion” (PTP) (described, e.g., in U.S. patent application Ser. No. 10/338,046, filed Jan. 6, 2003, entitled “Head-Disk Interference Detection Method and Apparatus,” which is incorporated herein by reference) is affected by temperature in the HDD and is particularly strongly related to temperature of the HDA of the HDD. Magnetic over-write, which affects the HDD error rate margin, is also a function of temperature. In fact, increasing the write current, at all temperatures, to overcome the over-write problems will generally exacerbate the clearance problem. Accordingly, design margins for head-disk clearance and/or magnetic performance of the head and disk are affected by the temperature, particularly the HDA temperature, of the HDD.
Devices and procedures have been developed which can at least partially compensate for such thermal effects with a reasonable degree of success. However, the success of such compensation is related to the accuracy of (substantially) real-time knowledge of the HDA temperature. Accordingly, it would be useful to provide a method and apparatus for estimating temperature (especially for supporting areal density growth at expected costs and reliability) in a manner which provides temperature estimates which are sufficiently accurate, reliable, frequent and low-lag, preferably in a cost-effective manner.
It is possible to add one or more discrete (non-integrated) temperature sensors to the HDD for such purposes. Examples include thermistors or thermal-diode circuits. In general, discrete sensors would be connected to an analog-to-digital converter (ADC), e.g., via multiplexing switches to enable the HDD processor to convert the sensor output to an HDA temperature estimate. Some discrete sensors have a built-in ADC but are often avoided because of cost. The conversion to the HDA temperature can be, e.g., very simple scaling and can include sensor calibration and linearization. To use such discrete sensors for estimating HDA temperature, the sensor would be best located in the HDA. If, instead, a discrete sensor is positioned on the PCB, in order to retain a degree of correlation of the sensor to the actual HDA temperature, the discrete sensor should be located as close as feasible to the HDA (e.g., on the side of the PCB facing the HDA, preferably isolated from external heat sources and/or airflow). Although discrete sensors can be used to estimate HDA temperature, it is believed that the cost of this approach is undesirably high. High costs associated with the discrete sensor approach are associated not only with the incremental cost of the sensor but also packaging constraints, added parts (that can reduce reliability and yield), and other potential problems. Accordingly, it would be useful to provide HDA temperature estimates while avoiding undesirable costs such as those associated with using discrete sensors.
One approach to avoiding the incremental costs associated with discrete sensors would be to make use of one or more sensors which are already present in the HDD, for another purpose. For example, many HDD's employ application specific integrated circuits (ASIC's) which have integrated heat sensors. These sensors, which are typically integrated versions of discrete thermal-diode circuits, are commercially available and are typically provided by ASIC vendors for purposes such as confirming operating power and thermal resistance of packaging, e.g., during development. Some HDD manufacturers make use of such integrated sensors during system design, e.g., to enhance reliability. Because such integrated sensors are provided by the ASIC manufacturer for specific purposes, it is not surprising that the output of such sensors are more directly indicative of the ASIC die temperature than, e.g., ambient temperature. The dynamic thermal response of the die, its package and the method of heat sinking also filter the observable sensor output, so that the output is, in general, more directly indicative of die temperature and less directly indicative of temperature at a location different from the ASIC die (such as ambient temperature in the HDA). Furthermore, the temperature of the ASIC die can fluctuate rapidly in response to changes in ASIC operating power (such as fluctuations resulting from changes in operating mode). Accordingly, it would be useful to provide a temperature estimator which can estimate temperatures at a distance from the sensor, e.g., by accounting for factors which affect sensor temperature.
One possible approach to using a sensor to estimate a temperature at a distant site would be to maintain the system or components thereof (such as the HDD pre-amp) in a predetermined operating mode for a period of time. For example, in one approach the pre-amplifier would be forced to a “read” mode for a sufficient time so that thermal transients expire (in at least some designs this would be a period of about 5 seconds). Such an approach, however, imposes severe command latency penalties on HDD performance whenever a temperature estimate is needed (which may be, for example, about once every 5 minutes). Although, for some applications, this type of latency would only have a small impact, for other applications (e.g., video-streaming or audio-streaming) such command latency usually would be unacceptable. Accordingly, it would be useful to provide a method and apparatus for estimating temperatures which could avoid the need to force an operating mode periodically or frequently (e.g., each time a temperature estimate is needed).
Another approach would be to force the system (or its components) to a pre-defined operating mode as described generally above, but to perform such procedure only when this would not interfere with desired or requested HDD usage. For example, rather than making a temperature estimate as needed, HDA temperature estimates would be delayed, e.g., until activity is low enough to allow a good reading. A difficulty with this approach is that, by using a previous temperature estimate until such time as it is convenient to obtain a new (accurate) estimate, there may be a relatively long delay until such convenient time occurs. Thus, the most recent previous temperature estimate (still) being used may significantly depart from the actual HDA temperature. Accordingly, it would be useful to provide a temperature estimate method and apparatus which is frequent enough to be sufficiently representative of actual temperature, without the need to delay or interrupt HDD read and write commands.